1. Field of the Invention
The present invention relates to a binary code symbol for non-linear strain measurement. More specifically, the invention relates to an improvement of the binary code symbol for non-linear strain measurement that is the subject of co-pending U.S. Published Application No. 2006-0289652-A1 (application Ser. No. 11/167,558, filed Jun. 28, 2005) for “Binary Code Symbol for Non-Linear Strain Measurement and Apparatus and an improvement of Method for Analyzing and Measuring Strain”; and in particular, additional examples of binary code symbol formats that can encode a range of data values using an error-correcting code (ECC) technique.
2. Related Art
There are numerous one-dimensional (1D) and two-dimensional (2D) symbols in use today, and most utilize a majority of the symbol's surface area to store the encoded information. These symbols are typically comprised of large, distinguishable blocks, dots, or bars called “cells” that enable data encoding. The spacing, relative size, state (i.e. black or white), or some combination of cell attributes is exploited to encode and decode data. These types of symbols are designed for inexpensive, low-resolution reading devices (or sensors); therefore cell dimensions can be relatively large with respect to the overall symbol size.
While many applications require that a symbol's encoded information be “read,” there are additional applications that warrant a detailed accounting of the symbol's spatial characteristics. Metrology is one such application, which involves making precise geometric measurements of the symbol's features. Symbols optimized for “reading” purposes are not necessarily, nor are they normally, optimized for “metrology” purposes.
Examples of common symbols are a UPC symbol, a Data Matrix symbol, and a MaxiCode symbol, which are shown in FIGS. 1A-1C of U.S. application Ser. No. 11/167,558, the disclosure of which is incorporated herein by reference in its entirety. As shown in FIGS. 1A-1C of U.S. Published Application No. 2006-0289652-A1, typical 1D and 2D symbols utilize cell arrangements that result in a broken (or non-continuous) symbol perimeter. Additionally, each has cells that are distributed somewhat uniformly across the entire symbol area. These characteristics are an efficient use of the symbol's surface area as a data encoder/decoder, but can cause a reduction in accuracy for certain types of deformation analyses, e.g. strain measurement.
Sensor resolution for machine-enabled metrology is typically higher than the sensor resolution required to simply encode and decode symbol information. Therefore with high-resolution sensors, it is possible to relax some of the “reader” requirements placed on existing symbol design, and produce symbols specifically for deformation/strain measurement.
It is to the solution of these and other problems that the present invention is directed.